The present invention relates to a cylinder head gasket to be installed between two members, such as a cylinder head and a cylinder block of an internal combustion, to seal therebetween.
When the joint surfaces of the cylinder head and cylinder block (cylinder body) of an automobile engine is sealed, a metal cylinder head gasket is installed between the cylinder head and cylinder block and seals combustion gas, coolant water, lubricating oil, and so on.
The above-mentioned cylinder head gasket has been changed from a lamination-type metal cylinder head gasket wherein multiple sheets of metal substrates are laminated, to a cylinder head gasket with a simple structure formed by one or two metal substrates for the needs of a lightweight engine, manufacturing cost reduction, and so on. Since the cylinder head gasket is formed by one or two metal plates, and usable materials are also limited in terms of the lightweight engine, the type and number of sealing means are also limited. As a result, a relatively simplified sealing means has to be used.
Also, in recent lightweight and small-sized engines, engine rigidity has been decreased, so that in the sealing of the cylinder head gasket, providing a uniform sealing surface pressure around a cylinder bore has become difficult. More specifically, due to a structural problem around the cylinder bore of an engine member, when the gasket is tightened, there is a shortage of sealing surface pressure at the portion where the rigidity is weak. As a result, there has been a number of gas leaks in the portion where the rigidity is weak.
When even a small amount of the leaked gas penetrates a water hole or oil hole, the circulation of water or oil is blocked due to the invasion of the gas in a liquid such as water, oil, and so on. This blockage interferes with the cooling of the engine, and causes engine trouble, so that adequate measures are required.
On the one hand, when a large sealing surface pressure is provided in the nearest peripheral part of the cylinder bore in order to assure the sealing performance of the bore, the deformation of the cylinder bore with low rigidity is accelerated, and the sealing means of the gasket does not function well. As a result, it is difficult to achieve adequate sealing performance.
Most of the gas leakages of the cylinder head gasket occur between the bores which are the portions where the load by a tightening bolt becomes weak; and on the exhaust side. More specifically, while the area of a tightening bolt hole has a large tightening load and generates excessive sealing surface pressure, the sealing surface pressure in other parts is reduced more for that, and the overall surface pressure distribution becomes unequal. The occurrence of the portion where the surface pressure is weak in the unequal surface pressure distribution causes the leakage of the combustion gas.
In order to solve the above-mentioned problem, a metal laminate gasket is proposed, wherein the width of a metal ring being inserted into a folded portion (grommet) of the cylinder bore is formed widely in such a way as to project near the tightening bolt hole from the folded portion rather than between the tightening bolt holes. The metal laminate gasket generates a well-balanced surface pressure distribution by dispersing a tightening load due to the tightening of the tightening bolt (for example, refer to Japanese Patent Publication 1).
However, although this structure has the effect of adjusting the surface pressure distribution in the folded portion, the surface pressure distribution in the bead portion cannot be adjusted.
Also, a meandering-shape portion such as a wave shape and so on in a plan view may be provided between the tightening bolt holes in the circumferential direction of the bead around the cylinder bore. However, in this case, there are problems that relatively high construction accuracy is required for a metal mold for forming the meandering portion; and the folded portion cannot be provided around the cylinder bore due to the obstacle of the meandering portion.
[Patent Document 1] Japanese Patent Publication No. 10-252894
The present invention is made in order to solve the above-mentioned problems, and the object of the invention is to provide a cylinder head gasket being able to improve the sealing surface pressure between the cylinder bores or in the intermediate portion between the tightening bolt holes on the exhaust side wherein the sealing performance of the cylinder head gasket is easily lowered, in a relatively simple structure.
Further objects and advantages of the invention will be apparent from the following description of the invention.